In radiosurgery, very intense and precisely collimated doses of radiation in a beam from a source outside a patient's body are delivered to a target region in the body, in order to destroy lesions. Typically, the target region consists of a volume of tumorous tissue. Radiosurgery requires an extremely accurate spatial localization of the targeted lesions. Radiosurgery offers apparent advantages over conventional surgery, during which a surgeon's scalpel removes the lesion, by avoiding the common risks and problems associated with open surgery. These problems include invasiveness, high costs, the need for in-hospital stays and general anesthesia, and complications associated with post-operative recovery. When a lesion is located close to critical organs, nerves, or arteries, the risks of open surgery are even greater.
As a first step in performing radiosurgery, it is necessary to determine with great precision the location of lesion and any surrounding critical structures, relative to the reference frame of the treatment device. Computed tomography (“CT”), magnetic resonance imaging (“MRI”) scans, and other imaging modalities enable practitioners to precisely locate a lesion relative to skeletal landmarks or implanted fiducial markers. However, it is also necessary to control the position of the radiation source so that its beam can be precisely directed to the target tissue while avoiding adjacent critical body structures.
Thus radiosurgery necessitates high precision diagnosis and high precision radiation source control. The consequences of deviating outside the prescribed tolerances for the diagnosis and the radiation source control can be potentially devastating to a patient. Accordingly, quality assurance mechanisms should be integrated into a radiation treatment delivery system to ensure proper alignment and configuration of the system prior to delivering a prescribed radiation dose to a patient.
Conventional quality assurance mechanisms include pointing the radiation source at an alignment marker, delivering a radiation dose to the alignment marker, and then analyzing the alignment marker itself to determine if the prescribed dose was actually delivered to the correct location. If the prescribed dose was delivered as expected, then the radiation treatment delivery system is deemed properly aligned. If the prescribed dose was not delivered as expected, then the radiation treatment delivery system is deemed misaligned. Conventional alignment markers include silver loaded gels capsules or photographic film canisters that can store readable information about the distribution of the radiation dose delivered to the alignment marker. However, extracting this alignment information from silver loaded gels or photographic film canisters located within the alignment marker itself is a time consuming and costly task.